Twitter is replacing its head of product. Again.

The company doesn't have a permanent replacement lined up.

Twitter's consumer product boss Jeff Seibert, who just took over Twitter's core product team back in September, is no longer running Twitter product, according to multiple sources. Seibert, who co-founded Crashlytics, will go back to running Twitter's developer product suite Fabric, which he was doing before the promotion in the fall.

Twitter does not have a permanent replacement for Seibert, and is opening up a search to fill the role, according to sources. Ed Ho, a senior engineering director who has been at Twitter for two years, will take over Twitter's product on an interim basis.

"This year we're focused on delivering on five product priorities — refining our core service, live-streaming video, creators, safety, and developers — as well as recruiting great talent. We've successfully increased our shipping cadence on our core service and have asked some of our top leaders to take on key roles in the other priority areas."

Seibert was the fourth person to run Twitter's core product since early 2014. He took over the day-to-day consumer product responsibilities from then-VP of Product Kevin Weil, who would later move on to take the same role at Instagram as part of a massive executive exodus from Twitter in January. Seibert's appointment was the first major restructuring move by CEO Jack Dorsey, who was still technically "interim" CEO at the time.

Now Seibert is out, or at least relocated, and joins a long list of Twitter product bosses who have either left or been pushed out in the past two years. It's a position that Twitter can't seem to lock down — The Verge's Casey Newton once likened it to the Defense Against the Dark Arts post in the "Harry Potter" series, where no professor seems to survive longer than a year.

That, of course, is a major problem for any consumer tech company, but especially for Twitter, which is having a tough time adding new users, thanks in large part to a product that many people think is too hard to use. Dorsey has been vocal about the need to change that, but it will be hard without a stable, permanent product leader in charge.

As part of the change, Twitter is also adding a new branch to its product team, which will work with and help important users and influencers who create content for Twitter. The team will be led by engineering VP Jeremy Rishel, who joined Twitter in 2013 when it acquired Bluefin Labs.